WO2007085077A1 - Coated metal oxide particles with low dissolution rate, methods for preparing same and use thereof in electrochemical systems - Google Patents

Abstract

The invention concerns particles comprising a core and a coat covering at least part of the core surface. The core consists for more than 50% of an acidic metal oxide and the core coating is based on a polymer, preferably based on a soiled polymer with high electrochemical stability. The particle has a solubility rate (ts), in fixed time, of the metal oxide migrating towards the electrolyte, per cycle, which is less than 5 per 10000. The particles are obtained by mixing the polymer and a metal oxide, via dry process with addition of solvent. The electrodes constituting an electrode substrate at least partly coated with a mixture consisting of at least 40 of those particles have remarkable electrochemical properties, in particular regarding the lifetime of batteries in which they are incorporated.

Description

 METALLIC OXIDE PARTICLES COATED AT LOW LEVELS OF

DISSOLUTION, METHODS OF PREPARATION AND USE IN

ELECTROCHEMICAL SYSTEMS

FIELD OF THE INVENTION

The present invention relates to particles comprising a core, based on acid metal oxide, whose surface is at least partially covered by a polymer having an electrochemical stability greater than 3.7 volts.

The present invention also relates to processes for the preparation of a mixture of these particles and which notably implement steps of mixing the constituents of the particles.

These particles have the advantage of a low level of solubility of the metal oxide present in the core, even after having been subjected to a large number of electrochemical cycles.

Among the many possible applications for the particle mixtures of the invention, there can be mentioned the covering of the electrode supports. The electrodes thus obtained are particularly stable in operation and can thus be advantageously used in high performance electrochemical systems.

The electrodes and generators thus obtained are also an object of the present invention, as are the processes for the preparation of the electrodes and generators of the invention.

HISTORICAL

The paper "Study of Mn dissolution from LiMn ₂ O ₄ spinel electrodes using in situ total reflection X-ray fluorescence analysis and XAFS fluorescence Technical "Yasuko Terada in Journal of Power Sources 97-98 (2001), pages 420-422, thus highlights the phenomenon of dissolution of LiMn ₂ O ₄ oxides in secondary batteries and the loss of capacity that results.

The paper "In situ XAFS study of the electrochemical deintercalation of Li from Lii _-x Mn ₂ - _y Crθ _4" Izumi Nakai et al. in Journal of Power Sources 97-98 (2001), pages 412-414, also describes the phenomenon of dissolution of the metal oxide and proposes to partially remedy the instability of the structure by the partial substitution of Mn by Cr, Co or Ni. This technique is complex and has disadvantages because it requires a new synthesis and adjustment of the dopant so that the structure is electrochemically stable.

The document "Influence of the particle size on the electrochemical properties of lithium manganese oxide" by Chung-Hsin Lu et al. in Journal of Power Sources 97-98 (2001), pages 458-469, highlights the role played by the particle size of lithium manganese oxides on the specific capacity values and on the Coulomb efficiency of metal oxide particles. lithium manganese.

In recent years, the commercial interest of metal oxides such as LiV ₃ Os, V ₂ O ₅ and LiMn ₂ O ₄ as constituent and functional elements of electrochemical systems has been very limited. This limitation stems in particular from the low stability of the metal oxides in the context of discharged charge cycles and the resulting significant losses of performance.

There was therefore a need to valorize such metal oxides considered as unstable, especially those with good electrochemical properties, such as LiMn ₂ O ₄ , LiV ₃ O ₈ , and moderate production costs, in particular because of a particular natural abundance . SUMMARY

A first object of the present invention is constituted by particles comprising a core and a coating which covers at least partly, preferably at least 80%, more preferably at least 90% and in the most advantageous manner 100% of the surface of said core, said particle being characterized in that:

said core is preferably composed for at least 90%, more preferably still for at least 94% by weight of an acid metal oxide, with a pH of preferably less than 6.5, more preferably still with a pH of between 3 and 6;

- The coating of the core being based on a polymer, preferably based on a salt polymer, whose electrochemical stability is greater than or equal to 3.7 volts; the size of the coating is of average thickness preferably between 500 nanometers and 2 micrometers and the coated core is of an average size of ₅ o which is preferably between 500 nanometers and 40 micrometers, more preferably still this size is between 2 and 20 micrometers; and the solubility rate (ts), at a fixed time, of the metal oxide migrating towards the electrolyte, per cycle, is less than 5 per 10,000, preferably this level is between 2 and 4.5 per 10,000.

According to an advantageous embodiment of the invention, the polymer used to carry out the coating is preferably chemically stable, or very stable, or even extremely stable.

Preferably, the electrochemical stability of the polymer used for the coating is between 3.75 and 5 volts.

A preferred subfamily of particles of the invention consists of particles whose metal oxide is selected from the group consisting of - AT -

LiMn ₂ O ₄ , V ₂ O ₅ , LiMn ( _2-x) V _x O ₄ with x ranging from 0 to 1 inclusive, V ₆ Oi ₃ , and LiV ₃ O _{8, more} preferably the metal oxide is LiV ₃ O ₈ .

According to an advantageous variant, the core of the particle comprises from 1 to 12%, preferably from 6 to 10% by weight, of a carbon chosen preferably from the group consisting of ethylene black, natural graphite and graphite. artificial, Shawinigan carbon, Ketjen carbon, and mixtures of at least two of these.

Another advantageous sub-family of particles of the invention may consist of particles whose core is based on one or more salty polymers, preferably based on at least one polymer salted by at least one selected salt. in the group consisting of LiFSI, LiTFSI, LiBETI, LiDCTA, LiBF ₄ and LiPFβ type salts; and at most 10% of fillers preferably selected from the group consisting of SiO ₂ , ZrO ₂ and Al ₂ O ₃ , and mixtures of at least two of these.

Advantageously, the polymer constituting the coating may be electronically conductive, and may preferably be based on a polymer selected from the group consisting of polyanilines, preferably from the group of polyanilines having an average molecular weight greater than 1000, and preferably between 2500 and 50000.

The constituent polymer of the coating may be non-electronically conductive and may advantageously be chosen from the group consisting of non-conducting polymers of the multi-branch type.

Preferably, the electron-non-conductive polymer is at least 3 branches, and even more preferably of the 4-branch type, such as those described in the international application published on July 31, 2003 under WO 03/063287 (and more particularly on pages 5, 8). and 9), filed on behalf of Hydro-Québec, as well as in columns 1 and 2 of US Pat. No. 6,190,804 (Ishiko et al.) and which have hybrid acrylate terminations. (preferably methacrylates) and alkoxy (preferably alkoxy with 1 to 8 carbon atoms, more preferably still methoxy or ethoxy), or vinyl.

Advantageously, the metal oxide may be a mixture (50:50) of LiV ₃ Oe and V ₂ O ₅ .

Another advantageous sub-family of particles of the invention may be constituted by particles comprising a core of the metal oxide LiV ₃ Os of a size of 5 microns, covered for 80% of its surface by a coating consisting of the polymer 4-branch type and an average thickness of between 10 nanometers and 5 microns, preferably between 15 nanometers and 2 microns, characterized by a ts less than 5%.

Another advantageous subfamily of particles of the invention may consist of particles comprising a metal oxide core V ₂ O ₅ of a size of 5 microns, covered for 80% of its surface by a coating consisting of the polymer 4 branches and an average thickness of between 10 nanometers and 5 micrometers, preferably between 15 nanometers and 2 micrometers, characterized by a ts less than 4%.

A second object of the present invention is constituted by a process for preparing a homogeneous mixture of particles according to the first subject of the invention.

The preparation may advantageously be carried out by mixing the polymer and a metal oxide, dry without any addition of solvent, preferably in proportions by weight of 10 to 90%, preferably 40 to 80% for each of the constituents of the mixture, preferably the amount of metal oxide present in the mixture is greater than that of the polymer.

The preparation may also be carried out by homogeneous mixture of particles according to the first subject of the invention, in which the mixture is: - by preparing a mixture of the polymer and a metal oxide, preferably in proportions by weight of 10 to 90%, preferably 40 to 80% for each of the constituents of the mixture, preferably the amount of oxide metal present in the mixture is greater than that of the polymer; and

with addition to the solvent of at least one solvent selected from the group consisting of acetone, acetonitrile, toluene, MEK, NMP or mixtures of at least two of these, preferably the solvent used represents in volume of 10 to 80%, more preferably 20 to 70% of the total volume of the solvent and the mixture.

Advantageously, the mixture can be done by "milling lease", "sand mill", HEBM ("Hot Electron Bolometer Mixer"), mechanofusion, "agglomaster", Nobita ^® or by implementation of at least two of these techniques, preferably at a temperature between 10 and 40 ° C and, advantageously, in the presence of an inert gas selected from the group consisting of nitrogen, argon or dry air.

A third object of the present invention is constituted by the electrodes constituted by an electrode support, said support being preferably made of a metallic material or a conductive plastic material, and at least partially covered, preferably homogeneous by a mixture consisting of at least 40%, preferably 50 to 80% by weight of particles defined in the first subject of the invention or obtained by one of the processes defined in the second subject of the invention.

Preferably, in the electrodes of the invention, at least one polymer is a binder of said electrode by creating bridges between the electrode support, the metal oxide-based particles and the polymer-based coating.

Advantageously, the binder polymer may be a mixture of a high stability polymer and binder and a binder polymer (polymer that binds the particles in the cathode) different from the polymer present in the coating. Preferably, the binder polymer may consist solely of a coating polymer with high electrochemical stability.

According to an advantageous embodiment of the invention, the electrodes may comprise at least one polymer containing at least one lithium salt and at least one carbon having a specific surface area greater than or equal to 1 m ² / g, preferably with a higher specific surface area. at 50 m ² / g.

Preferably, the mixture (polymer-oxide-salt-carbon) is produced without the addition of a solvent, advantageously by using the Doctor Blade method and / or by extrusion.

According to another advantageous embodiment, the mixture (polymer-oxide-salt-carbon) is produced with the addition of a solvent preferably chosen from the group consisting of acetone, acetonitrile, toluene, MEK, VC, DEC, DMC, EMC, DME or mixtures of at least two of these, preferably by using the method of the Doctor Blade and / or by extrusion.

Advantageously, the composition of the polymer may represent from 1 to 70% by weight relative to the total weight of the mixture (polymer + salt + oxide + carbon).

The electrodes in which the carbon composition represents 1 to 10% by weight relative to the total weight of the mixture (polymer + salt + oxide + carbon) are particularly interesting.

Preferably, the concentration of salt, present in the mixture (polymer-oxide-salt-carbon), and expressed relative to the polymer, is between 0.1 M and 3 M, preferably between 0.7 M and 2 M .

Another family of electrodes of the invention may be constituted by the electrodes, in which the carbon present in the mixture (polymer- oxide-salt-carbon), is a mixture of a first carbon of graphite nature with a specific surface area of less than 50 m ² / g and a second carbon of large non-graphitic surface type whose specific surface area is greater than 50 m ² / g; the specific surface is measured according to the BET method.

Advantageously, the carbon present in the electrode is of VGCF carbon fiber type, mesophase ex, PAN (polyacronitryl).

Preferably, in the electrode, the salt is dissolved in the polymer and is selected from the group consisting of LiFSI, LiTFSI, LiBETI, LiPF ₆ and mixtures of at least two of these.

A fourth object of the present invention is constituted by the methods for preparing one of the electrodes defined in the third subject of the present invention.

According to an advantageous embodiment, an oxide-polymer-salt-carbon liquid mixture can be spread on a metal-type current collector by extrusion or by "Doctor Blade", "slot die", "coma".

According to an advantageous embodiment, the polymer may be of the four-branch type with preferably at least two branches capable of giving rise to crosslinking, and it is converted into a polymer matrix, optionally in the presence of an organic solvent, by crosslinking. after spreading the mixture on the electrode support.

The crosslinking can advantageously be carried out without the addition of a crosslinking agent other than the metal oxide.

According to another advantageous variant, the polymer may be of EG type, with preferably at least two branches capable of giving rise to crosslinking, and it is converted into a polymer matrix, optionally in the presence of an organic solvent, by crosslinking after spreading. of the mixture on the electrode support. A fifth object of the present invention is constituted by a method for preparing electrochemical generators comprising at least one anode, at least one cathode and an electrolyte, in which at least one of the electrodes is as defined in the third subject of the present application. or as obtained by one of the methods defined in the fourth subject of the present invention.

Advantageously, these methods can be applied to the preparation of electrochemical generators of the lithium generator type and the spread cathode can be introduced into said lithium generator with a dry polymer as electrolyte, the battery contains no liquid solvent.

According to an advantageous embodiment, these processes can be applied to the preparation of electrochemical generators in which the electrolyte is made of the same material as the binder and the coating.

Advantageously, the process can be used for the preparation of electrochemical generators in which the electrolyte: consists of a material different from that which constitutes the binder and / or the coating; and or

also acts as a separator and consists of a dry polymer which has an electrochemical stability greater than 3.7 volts; and or

also acts as a separator and consists of a dry polymer which has an electrochemical stability of less than 3.7 volts.

Advantageously, the process can be used for the preparation of electrochemical generators in which:

the anode is of lithium or lithium or carbon alloy type, graphite, carbon fiber, Li ₄ Ti ₅ O ₁₂ , WO ₂ , preferably metallic lithium or slightly alloyed lithium; and or

the lithium is alloyed with Al, Sn, carbon, Si, Mg and the alloy metal content is greater than 50 ppm, preferably greater than 500 ppm. A sixth object of the present invention consists of the electrochemical generators obtained by implementing one of the methods defined in the fifth subject of the present invention.

Another advantageous family of the generators of the invention may be constituted by those comprising particles as defined in the first subject of the invention or as obtained by implementing a method according to the second subject of the invention. .

A seventh object of the present invention is constituted by the use of a generator, as defined in the sixth subject of the present invention, in an electric vehicle, in a hybrid vehicle, in telecommunications, UPS, and in devices electrochromic.

An eighth object of the present invention is constituted by the processes for reducing the solubility of metal oxides in electrochemical systems consisting in increasing the pH of the oxide, preferably by choosing the nature and the quantity of the carbon mixed with the particles of oxides, more particularly by coating the oxide particles with a polymer, based on PEO, polyacrylonitrile, PMMA and / or PVC solubilized in a solvent (acetonitrile, water, acetone, methanol, etc.), then drying the composition and charring at a temperature of about 600-700 ⁰ C, under an inert atmosphere for 8-12 hours; the quantity and type of the polymer used being related to the residual carbon content present at the surface of the particles of the oxide, and the oxide and polymer solution mixture being advantageously produced by Jar mill, mill bar, or paint mixer.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the phenomenon of dissolution observed for small particles, uncoated, based on lithium vanadium oxide and LiV ₃ O ₈ formula. Figure 2 illustrates the phenomenon of dissolution of large particles, uncoated, based vanadium oxide lithiated.

Figure 3 illustrates the mechanism of general formation of dendrites, upon the dissolution of an acidic metal oxide in an electrochemical system of the solid polymer lithium battery type.

Figure 4 shows the behavior of an electrode according to the invention, wherein the particles of the metal oxide have been coated with a stable polymer which slows the dissolution of vanadium in the electrode.

Figure 5 illustrates the device used to detect the oxidation current of a metal oxide and to quantify the limit of the operating voltage of the polymer.

FIG. 6 gives the results, in the form of curves, of the measurement of the stability of metal oxide particles LiVaOs coated respectively with a polyether polymer with a molecular weight MW of 70000, in the first case, and by a polymer with 4 branches, in the second case.

FIG. 7 represents the evolution of the chemical stability of the polyether polymer with a molecular weight MW of 70000, for a heat treatment of 1 day, 3 days, then 1 week, and 2 weeks.

Figure 8 show changes in chemical stability of the polymer ERM-4B which is a macromonomer having four branches, of an average molecular weight MW of 10 000, a viscosity of 3.5 Pa. Sec at 25 ⁰ C and characterized by a number of acrylate functions per molecule which is 3, for a heat treatment of a duration of 3 days, the various curves corresponding to stability measurements carried out for a heat treatment of 1 day, 3 days, then 1 week , 2 weeks and the observation of crosslinking. FIG. 9 represents the evolution of the chemical stability of the polymer EG-2500 marketed under the trademark Elexcel, which is a hyperbranched macromonomer, polyoxyalkylene glycol acrylate whose number of acryl groups per molecule is 1.5, of a molecular weight average MW of 2500 and which is characterized by a viscosity of 0.3 Pa. sec at 25 ° C., the various curves corresponding to stability measurements made for a heat treatment of 1 day, 3 days, then 1 week, and 2 weeks, as well as the finding of crosslinking.

DETAILED DESCRIPTION OF PREFERRED ACHIEVEMENTS

As used in the context of this disclosure, the term "salt polymer" refers to a polymer that contains a salt such as a polymer salted with at least one salt selected from the group consisting of LiFSI salts. , LiTFSI, LiBETI, LiDCTA, LiBF ₄ and LiPF ₆ .

As used in the context of this disclosure, the term "electrochemical stability" corresponds to the window of stability of the polymer; outside this window, the polymer is degraded.

As used in this disclosure, the term "3-arm polymers" is related, as illustrated in the document "Relationship between Structural Factor of Gel Electrolyte and Characteristics of Electrolyte and Lithium-ion Polymer Battery Performances" by Hiroe Nakagawa et al., The 44th Symposium in Japan, Nov 4-6, 2003, Abstract 3D26, to three-branched polymers in the form of a 3-limbed comb. The 3 substantially parallel branches of these polymers are preferably attached to the center and both ends of a small skeleton, preferably having 3 atoms, preferably 3 carbon atoms, in the chain.

In the case of a chain with 3 carbon atoms, each of these atoms is connected to a branch. Among these polymers with 3 branches, and in the context of the present invention, those having a mean molecular weight (MW) ranging from 1000 to 1,000,000 are preferred, more preferably those whose average molecular weight ranges from 5,000 to 100,000.

As used in the context of this disclosure, the term "four-branched polymers" is related to the aforementioned patent application WO 03/063287, which is incorporated by reference into the present application, which describes a preferred family of polymers. four branches.

Such polymers have the form of a comb with 4 branches. The 4 substantially parallel branches of these polymers are respectively fixed between the two ends (preferably fixed to the chain symmetrically) and at both ends of a small chain, preferably consisting of a chain comprising 4 atoms which are preferably 4 carbon atoms.

In the case of a chain with 4 carbon atoms, each atom is connected to a branch.

Such polymers preferably have hybrid termini, more preferably hybrid terminations acrylates (preferably methacrylate) and alkoxy (preferably alkoxy with 1 to 8 carbon atoms, more preferably still methoxy or ethoxy), or vinyl, a branch at least said four-branched polymer (and preferably at least two branches) being capable of giving rise to crosslinking.

Preferably, the four-branched polymer is one of those defined in columns 1 and 2 of the aforementioned US-A-6, 190,804, which is incorporated by reference in the present application.

This polymer is preferably a polyether star polymer which has at least four branches having terminations containing the following functions: acrylate or methacrylate and alkoxy, allyloxy and / or vinyloxy, at least one, and preferably at least two of these functions are active to allow crosslinking.

Other families of polyethers whose molecular mass is greater than or equal to 30,000 are advantageously used in the context of the present invention.

According to another preferred embodiment of the present invention, the 4-branched polymer is a tetrafunctional polymer preferably of high molecular point corresponding to formula (I):

R ¹ R ² R ³

I I I

- (CH ₂ CHO) _m - (CH ₂ CHO) _n - CO- C = CH ₂

wherein R ¹ and R ² each represent a hydrogen atom or a lower alkyl (preferably 1 to 7 carbon atoms); R ³ represents a hydrogen atom or a methyl group; m and n each represents an integer greater than or equal to 0; in each high molecular point chain, m + n>35; and each of R ¹ , R ² , R ³ and each of the m and n parameters may be the same or different in the 4 high molecular weight chains.

Among these four-branched polymers, those having an average molecular weight of between 1,000 and 1,000,000, more preferably still those having an average molecular weight ranging from 5,000 to 100,000 are particularly interesting.

According to another preferred embodiment, star-type polyethers of at least four branches with a hybrid termination (acrylate or methacrylate and alkoxy, allyloxy, vinyloxy) are retained. Its stability voltage is much higher than 4. Also the EG-type vinyl polymers and more particularly those described in the patent application published in EP-A-1, 249,461 (Wendel et al.), Which is incorporated by reference in the present application, are of particular interest as protective material. Particularly advantageous among these polymers are those whose average molecular weight ranges from 600 to 2500.

Polymers of this family may advantageously be obtained by reacting ethylene oxide and propanol-1-epoxy-2,3 with the starting material, or by reacting propanol-1-epoxy-2,3 with ethylene glycol as the starting material for producing a polymer compound. This step is followed by the introduction of polymerizable and / or non-polymerizable functional groups at each end of a backbone and side chains into the resulting polymeric compound.

Compounds having one or more active hydrogen residues and alkoxide may also be used as starting materials.

Examples of active hydrogen residues for the compound having one or more active hydrogen residues include the group of hydroxyls, preferably having from 1 to 5 active hydrogen residues. Specific examples of compounds having one or more active hydrogen residues include triethylene glycol monomethyl ether, ethylene glycol, glycerin, diglycerin, pentaerythritol and their derivatives.

Specific examples of alkoxide also include CH ₃ ONa, t-BuOK and their derivatives.

The polyetheric polymer compounds of the invention have the unit of structure represented by the formula (1) as well as the unit of structure represented by the formula (2) and / or the unit of structure represented by the formula (3) . The number of structural units represented by the formula (1) in a molecule is from 1 to 22,800, more preferably from 5 to 11400, and more preferably from 10 to 5700. The number of structural units of the formula ( 2) or (3) (but when both are included, the total number) is 1 to 13,600, more preferably 5 to 6800, and more preferably 10 to 3400 as well as a molecule.

d) (2) (3)

CH ₂ O CH ₂ O

I

I I

- CH ₂ CH ₂ O - - CH ₂ - - CH - CH

IIO - CH ₂ O

Examples of polymerizable functional groups introduced at each molecular end include (meth) acrylate residues, allyl groups and vinyl groups, and examples of non-polymerizable functional groups include alkyl groups or functional groups comprising boron atoms.

Like the above alkyl groups, alkyl groups having 1 to 6 carbon atoms are preferred, those having 1 to 4 carbon atoms are more preferred, and the methyl groups are especially advantageous.

Examples of functional groups comprising boron atoms include those represented by the following formulas (4) or (5):

(4) (5)

R ¹¹ R ²¹

/ I - B _ B ^" - R ²² X ⁺

\ I

R ¹² R ²³ R ¹¹ , and R ¹² in formula (4) and R ²¹ , R ²² , R ²³ in formula (5) may be the same or different, and each represents hydrogen, halogen, alkyl, alkoxy, aryl, alkenyl, alkynyl , aralkyl, cycloalkyl, cyano, hydroxyl, formyl, aryloxy, alkylthio, arylthio, acyloxy, sulfonyloxy, amino, alkylamino, arylamino, carbonamino, oxysulfonylamino, sulfonamide, oxycarbonylamino, ureide, acyl, oxycarbonyl, carbamoyl, sulfonyl, sulfinyl, oxysulfonyl, sulfamoyl , carboxylate, sulfonate, phosphonate, heterocyclic, -B (R ^a ) (R ^b ), - OB (R ^a ) (R ^b ) or OSi (R ^a ) (R ^b ) (R ^c ). (R ^a ), (R ^b ) and (R ⁰ ) each represent hydrogen, halogen, alkyl, alkoxy, aryl, alkenyl, alkynyl, aralkyl, cycloalkyl, cyano, hydroxyl, formyl, aryloxy, alkylthio, arylthio, acyloxy, sulfonyloxy , amino, alkylamino, arylamino, carbonamino, oxysulfonylamino, sulfonamide, oxycarbonylamino, ureide, acyl, oxycarbonyl, carbamoyl, sulfonyl, sulfinyl, oxysulfonyl, sulfamoyl, carboxylate, sulfonate, phosphonate, heterocyclic or derivatives thereof. R ¹¹ , and R ¹² in formula (4) and R ²¹ , R ²² , R ²³ in formula (5) may be bonded together to form a ring, and the ring may have substituents. Each group may also be substituted with substitutable groups. In addition, X ⁺ in formula (5) represents an alkali metal ion, and is advantageously a lithium ion.

The ends of the molecular chains in the polyether polymer may all be polymerizable functional groups, non-polymerizable functional groups, or may include both.

The average molecular weight (MW) of this type of polyether polymer compound is not especially limited, but is usually about 500 to 2 million, and preferably about 1000 to 1.5 million.

The polymers of these preferential families are moreover advantageously chosen from polymers which are crosslinkable by ultraviolet, infrared, heat treatment and / or electron beam ("EBeam").

According to the invention, it has unexpectedly been discovered that the acidic or basic nature of a metal oxide greatly influences its stability. So the Soluble oxides such as LiV ₃ Oa and V ₂ O ₅ are generally found to have acidic pH, whereas insoluble oxides such as LiFePO ₄ and LiCoO ₂ are found to have basic pHs.

Table I shows some pH values for metal oxides LiV ₃ O ₈ and LiCoO ₂ , in the presence of varying amounts of carbon, mixed with the oxide. The pH was measured using the method defined below.

Table I

Test Oxyde Ketjen Carbon Time PH Color (% W) (W%) sampling pH = 10.6 pH = 8.2 1 LiV ₃ O ₈ 5 30 4.52 Yellow

2 LiV ₃ O ₈ 3.75 30 4.44 Yellow

3 LiV ₃ O ₈ 2.5 2.5 30 5.5 Yellow

4 LiFePO ₄ 5 30 10.1 Colorless

5 LiFePO ₄ 3.75 30 10.06 Colorless

6 LiFePO ₄ 2.5 2.5 30 10.04 Colorless

7 LiFePO ₄ 30 9.9 Colorless

8 LiCoO ₂ 30 8.6 Colorless

According to the invention, it has also been discovered that a coating with a particular polymer makes it possible to very substantially improve the stability of the metal oxide particles at acidic pH.

Indeed, the difficulties encountered with soluble metal oxides have been solved by the method hereinafter explained and which is consistent with the main idea of the invention which consists in coating the stable metal oxide particle with a polymer of nature special.

Thus, by way of example, the LiV ₃ Os particles are protected by coating them with a chemically and / or electrochemically stable polymer in their window. electrochemical, with an electrochemical stability greater than or equal to 3.7 volts.

The polymers used to carry out the coating are preferably of the polyether type, more preferably of the multi branch or hyperbranch type, in particular those synthesized by the company DKS and described in US Pat. No. 6,190,804, which is incorporated by reference in the US Pat. this request.

These polymers are preferably salted with a salt of LiFSI, LiTFSI, LiBETI, LiBF ₄ and LiPF _{6 type} . For coating the oxide particles, a mixture (polymer with at least one salt) which is liquid at room temperature is preferably used.

According to an advantageous embodiment of the invention, the coating of the metal oxide particles is carried out by one of the following methods or by combination of at least two of the methods: "lease milling"; "jar milling"; HEBM

("High Energy Bail Milling"); mechano; by implementing the device

Nobulta marketed by the company Hosokawa, Japan; "Aggolmaster"; and

"pebble mill".

The coating of the oxide can be achieved by several methods, with or without a solvent.

The salty polymer coating the oxide particles plays multiple roles. Its first role is to ensure the non-dissolution of the metal oxide, such as LiV ₃ Os Its second role is that of binder, between the oxide particles present in the cathode spreading solution, for example on a support in aluminium. The third role is to ensure the ionic conductivity of the salt, between the particles, and through the separator.

The following parameters relating to the nature of the polymer used to carry out the coating play an important role in the stability ie in the weak dissolution of the acidic metal oxide: - electrochemical stability;

the chemical stability of the polymer; and the conductive or non-conductive character.

The various methods used for the quantification of the various parameters of the polymers used to carry out the coating of the metal oxide particles and to evaluate the stability of the particles of the invention are hereinafter defined.

Method for measuring the pH of the metal oxide

The pH of the metal oxide represents the measured value, using a conventional glass electrode, in an aqueous solution of the oxide obtained by dissolution, under normal conditions of temperature and pressure, of 0.15 grams of the oxide in 10 cc of water. It is allowed to stand for a week under normal temperature conditions, then stirred just before taking the measurement with an OAKTON 2100 series apparatus, marketed by OAKTON. In the context of the present invention, any sample whose pH is less than 7 is classified as acidic metal oxide.

It is noted that the nature and the percentage of the carbon present in the mixture (carbon-metal oxide) influences the value of the pH; it differs more or less substantially from that of the metal oxide alone. This parameter can be used to improve the stability of metal oxides.

In order to reduce the solubility and thus increase the pH of the oxide, the following particular method of coating the oxide particles with carbon is preferred. The oxide powder is coated with a polymer based on PEO, polyacrylonitrile, PMMA and / or PVC solubilized in a solvent (acetonitrile, water, acetone, methanol, etc.). Then the composition is dried and then carbonized at a temperature of about 600-700 ⁰ C under an inert atmosphere and for 8-12 hours. The amount of the polymer used is related to the residual carbon content present at the surface of the particles of the oxide. The mixture oxidizes and Polymer solution can be achieved by "mill jar", "mill lease", or paint mixer.

It has been demonstrated that soluble oxides generally have acidic pH, while insoluble oxides such as LiFePO ₄ and LiCoO ₂ have basic pH.

It has also been discovered that the marked instability observed for acidic metal oxides, present in electrochemical systems, is materialized by a migration of the soluble species to the anode while passing through the electrolyte and the films passivation positioned on the anode.

This negative phenomenon of dissolving the metal oxide and forming dendrites considerably reduces the physico-chemical properties of the passivation films. This phenomenon is visualized in Figure 3 which shows the operation of the battery and the pattern of uncontaminated lithium metal. This conclusion is directly derived from the experimental results of XPS ("X-

Ray-Photoelectron Spectroscopy "), after dissolution of vanadium that migrates through the solid polymer electrolyte (SPE).

FIG. 3 illustrates, in particular, the mechanism for the general formation of dendrites during the dissolution of an acid metal oxide in an electrochemical system of the solid polymer lithium battery type. SPE stands for Solid Polymer Electrolyte and SEI stands for Solid Electrolyte Interface (passivation film). The metal oxide particles, initially present only in the cathode, significantly decreased in size during the first 50 cycles and partially migrated into the SPE and the lithium anode. After 100 cycles, dendrites of the oxide were formed. These dendrites extend from lithium metal to lithium separator, while piercing the electrolyte. The references used in Figure 3 are: 2 for lithium (negative), 4 for SPE ("Solid Polymer Electrolyte" - separator), 6 for carbon, 8 for vanadium oxide, 10 for Li ₂ O, 12 for Li ₂ CO ₃ , 14 for dendrite and 16 for cathode.

A metal of the soluble oxide reacts with the lithium of the passivation film to make it an electronic conductor and increases its thickness. The formation of dendrites can result in the drilling of the SPE. And, when the dendrites reach a certain size, they can touch the cathode thus creating a short circuit that causes the battery to die.

Measurements carried out with a 4 cm ² laboratory type Lithium polymer battery of surface show that, during the cycling, in particular with a high current higher than C / 1 (discharge in 1 hour), no dissolution is manifested for the oxides non-soluble, which are basic in nature, whereas in the same stream the soluble oxides dissolve.

Method of measuring the electrochemical stability the metal oxide

This stability is measured by the method developed by the applicant using the device shown in Figure 3. A Mac battery is used with a potentiostatic mode to characterize materials in electrochemical stability. This is a slow cyclovoltametry test. When the scanning speed is 10 mV / h, the material is considered to be in its stable thermodynamic state. The current peaks generated are therefore in regions where there is no electrochemical activity. The degradation of the material is in regions where there is no electrochemical activity of the material. The degradation can intensify, depending on the voltage, to form a non-reversible electrochemical wall.

A degradation curve of the polymer is shown in FIG. 6. The beginning of the oxidation wall expresses the limit of stability of the polymer. It is thanks to the high surface area carbon electrode, such as Ketjen or Shawinigan, that the electrochemical stability can easily be measured and the polymer degradation detected. Method for measuring the electrochemical stability of a polymer

To detect the limit of the operating voltage of the polymer with the oxidation current, one uses the electrochemical method which is already used in the international application published under WO / 2003/063287 (which is incorporated by reference in the present application), the name Hydro-Quebec, and it is implemented using the device shown in Figure 5.

Figure 5 illustrates the device used to detect the oxidation current of a metal oxide and to quantify the limit of the operating voltage of the polymer. The references used in FIG. 5 are: 28 for lithium, 30 for SPE, 32 for Shawinigan carbon and 34 for binder (4-branched polymer).

The cathode used for the measurements is a polymer and carbon composite with a large surface area spread on an aluminum current collector. Thanks to the surface developed by carbon, this material acts as a detector and can detect any oxidation current with an intensity as low as about 2 microamperes. The electrolyte in solid form or in liquid form, soaked in a microporous polyolefin membrane, such as Celgard ^® , is stable at high voltage.

The anode is composed of metallic lithium which serves as reference electrode and as counter-electrode.

The electrochemical method used is the slow cyclovoltametry implemented with a scanning speed of 10 mV / h. This method illustrates the oxidation current as a function of the voltage: each time the current approaches zero, the operating voltage of the polymer is stable. The value of the electrochemical stability is defined as the value of the voltage applied to the system when one observes the abrupt change in the current / voltage (I function of V).

Chemical stability model as a preliminary test of the electrochemical stability of the coating polymer

The stability of the polymer used as the electrolyte in the cathode is determined by the preparation of a sample of spreading solution containing the oxide, the polymer, the salt and the spreading solvent. A sample of this solution is taken (0.3 grams) and put in a 40 ml sample bottle, the solvent is then evaporated by vacuuming the various samples overnight. The sample bottles are sealed, under an argon atmosphere, then transferred to an oven for treatment at 80 ^° C. A monitoring of the stability of the polymer as a function of time was carried out by dissolving the cathode in THF, then by injecting it after filtration in a GPC system to determine the molecular weight and polydispersity of the extracted polymer. These results are subsequently compared with the results of a polymer that has not undergone any heat treatment.

The results are shown in Figures 7 to 9 as comparative GPC curves. Figure 7 shows the evolution of the molecular weight of a standard polymer as a function of time, after heat treatment. This figure shows that after less than two hours, at 80 ^° C., in the presence of open circuit voltage (OCV) vanadium oxide at 3.55 volts, the polymer initiates a significant degradation. This degradation continues until the polymer is completely degraded. This step is reached in less than 2 days.

Figures 8 and 9 show the evolution of the molecular weight of new polymers (respectively ERM-4B and EG-2500) under the same conditions of degradation. These figures demonstrate, for these two polymers, that the extracted cathode samples remain stable for a period of more than 2 hours, at 80 ^° C. Subsequently, a decrease in the Although the molecular weight and polydispersity of the extractor remain stable. After more than 3 days ERM-4Branches (also called 4 branches) and one day respectively for the EG-2500, the polymers are fully crosslinked and show no signs of degradation. Only the by-products related to the crosslinking reaction are then extracted and analyzed by GPC.

By these stability analyzes, carried out at several temperatures, it is possible to conclude that the new polymers of the ERM-4B or EG-2500 type are considerably more stable to oxidation than a vanadium oxide and, with time it is possible to crosslink in situ these electrolytes, in the cathode, and that this network remains stable over several weeks at high temperature (80 or 110 ⁰ C).

In conclusion, it will be considered that a polymer is chemically stable if the decrease in its molecular weight, after having been subjected to a heat treatment at 80 ^° C. for 1 day, has not decreased by more than 10%.

Under these conditions, it is considered that a polymer is very stable if the decrease in its molecular weight is less than 5% under the same conditions.

An extremely stable polymer is considered to be one in which the reduction in molecular weight, after having been subjected to heat treatment at 80 ^° C. for 3 weeks, has not decreased by more than 5%.

The chemically stable polymers, preferably the moderately stable polymers and more preferably those classified, according to this test, as being very stable are advantageously used in the context of the present invention to constitute the coating of the soluble metal oxide particles. Definition of the solubility rate of a metal oxide present in the cathode of an electrochemical system

In the context of the present invention, the solubility rate (ts) of the metal oxide, at a fixed time, is the percentage of metal oxide particles initially present in the cathode that migrate to the electrolyte and to the anode. .

An example of implementation of the method for measuring the solubility rate of vanadium oxide and the method of calculating the vanadium dissolution rate is given below.

A sectional view of a lithium battery (Lithium / SPE / cathode) is observed under the microscope before cycling and after cycling.

Before cycling - thanks to EDX (Energy Dispersive X-rays) coupled on a scanning electron microscope that maps the map ("mapping") of the surface of the vanadium element in the cathode. This surface is considered as 100% reference and when analyzing the vanadium map on the separator (SPE) and lithium, no vanadium trace or surface is detected. We speak of 0% dissolved vanadium.

After Cycling - The surface of the map ("mapping") vanadium on the SPE and lithium is 5%, ie before cycling, the vanadium map of the cathode corresponds to a surface of 15 cm * 15 cm = 225 cm ² . After cycling the vanadium surface found on the SPE and the Lithium surface is 11.5 cm ² .

This count makes it possible to evaluate the level of vanadium which is equivalent to 5% of dissolved vanadium. Definition of the conductivity and / or non-conductivity criterion of a polymer

The electrical conductivity of a substance, also called the ability of a surface to conduct an electrical current, is defined as the inverse of the resistivity: σ = 1 / p. As the intensity of the electric field in the material is expressed by the relation E = V / L, Ohm's law can be written in terms of current density by the formula J = σE. Conductive metals are those whose σ> 10 ⁵ (Ω.m) ^'1 . We consider as semiconductor materials those which verify the relation: 10 ^{* 6} <σ <10 ⁵ (Ω.m) ^"1. We consider as insulating materials those satisfying the relation σ <10 ^{" 6} (Ω .m) ^"1 .

In the context of the present invention is classified as conductive polymers those having a conductivity greater than 10 ^{"5 (Ω.m)" 1} and as non-conductive polymers those having a conductivity of less than or equal to 10 ^"6 (Ω.m ) - ¹ .

Parameters for the Manufacture of Electrochemical Generators Incorporating Encased Metal Oxide Particles of the Invention

The generator or electrochemical battery is formed of at least 3 films, respectively playing the role of anode, electrolyte and cathode.

Anode - This is a film of lithium or lithium alloy, or lithium carbon. Preferably the film is lithium.

Electrolyte (SPE) - This is a dry polymer film without any solvents. Its nature depends on the oxide of the cathode.

For oxides operating from 1 to 3.6 volts

This case corresponds to the potential voltage at mid-discharge / 100 hours, the operating voltage of the oxide is connected to the potential at mid-discharge in C / 100 (discharge in 100 hours). For example: Li ₄ Ti ₅ Oi ₂ (1.5 Volts), LiV ₃ O ₈ (2.55 Volts). In this case, the SPE may be of the same nature as the coating polymer, or of a different type, ie characterized by a stability of less than or equal to 3.7 volts.

For oxides operating from 3 to 5 volts

In this case, the SPE should preferably be of the same nature as the polymer coating the oxide: for example LiCoO ₂ (3.6 volts) and / or LiFePo ₄ (3.5 volts).

Cathode - It is formed of a soluble or non-soluble oxide, preferably the oxide is soluble with a stable polymeric coating of electrochemical stability greater than or equal to 3.7 volts.

The binder can be of the same nature as the coating of the oxide, when the potential of the oxide varies from 3 to 5 volts.

EXAMPLES

The following examples are given purely by way of illustration and can not be interpreted as constituting any limitation of the objects of the present invention.

Table I above summarizes the preparation parameters of the particles according to Examples 1 to 11 which follow.

Example 1

A mixture of Shawinigan carbon (0.91 grams), with a polyether polymer P70 with a MW of 70,000 (2.63 grams) and with a LiTFSI salt (0.78 grams), is prepared. This mixture of 3 components is added to 27.3 ml of acetonitrile, the whole is homogenized in a Jar Milling for 24 hours.

The solution is spread on a 17 μm thick aluminum support using the Doctor Blade method. The electrode thus prepared is dried under vacuum at 90 ^° C. for 24 hours. An electrode 37 microns thick is obtained. This electrode is named P70-carb1.

A mixture of Shawinigan carbon (0.73 grams), Elexcel TA210 4-spoke polymer (2.06 grams) and LiTFSI salt (0.58 grams) was prepared. The 3 components of the mixture are then mixed with 28.9 ml of acetonitrile. Then the mixture is homogenized in a "milling jar" for 24 hours.

The solution is spread on an aluminum support using the Doctor Blade method. The electrode obtained will be dried under vacuum at 90 ^° C. The thickness of this electrode is 35 microns. This electrode is named 4B-carb1.

The battery is mounted as follows: - Lithium / Electrolyte 1 / 4B - Carbon 1 = CeI1 1 - Lithium / Electrolyte 2 / P70 - Carbon 1 = CeII 2

Lithium consists of a 55 micron thick film. The electrolyte 1 is of 4 branches nature with a thickness of 20 microns. The electrolyte 2 is of a P70 nature with a thickness of 20 microns.

The CeIM and Cell2 batteries are put in an oven at 80 ^° C. and connected to a Mac Pile in potentiostatic mode. Slow cyclovoltametry is applied to CeIH and Cell2, with a scan rate of 10 mV / hr.

The CeIM battery shows that the 4-branch polymer (Figure 6) is stable, up to a voltage of 4.1 volts. The Cell2 battery shows that the polymer P70 (FIG. 6) has a slight degradation wave around 3.3-3.6 volts, which is followed by a first peak of degradation at 3.74 volts.

Example 2 - with polymer P70

8.04 grams of LiV ₃ O ₈ , 0.43 grams of Ketjen carbon, 325 grams of P70 polymer and 0.90 grams of LiTFSI and 27 ml of acetonitrile are mixed in a "jar milling" for 24 hours after evaporation of the solvent. The results are shown in Figure 7 as a comparative GPC curve. Figure 7 shows the evolution of the molecular weight of the polymer, as a function of the duration of the heat treatment. This figure demonstrates that from two hours at 80 ^° C., in the presence of 3.55 V vanadium oxide, the polymer initiates a significant degradation. This degradation continues until the polymer is completely degraded, which is finally achieved in less than 2 weeks.

Example 3 - with polymer 4 branches

8 grams of LiV ₃ O ₈ , 0.42 grams of Ketjen carbon, 3.25 grams of 4-branched polymers and 0.90 grams of LiTFSI are mixed with 27 ml of acetonitrile for 24 hours in a "jar milling". .

After evaporation at 80 ^° C. of acetonitrile, the measurements carried out on the mixture of particles, which are reported in FIG. 8, demonstrate the evolution of the molecular weight of new polymers 4B, under the same degradation conditions. than in Example 2.

The figure demonstrates for this polymer that the extracted cathode samples remain stable for a period of more than 2 hours at 80 ° C. Subsequently, a decrease in the extraction rate is observed, although the molecular weight and the polydispersity of the extractant remain stable. After more than 3 days, ERM-4B is fully crosslinked and shows no sign of degradation.

Only the by-products related to the crosslinking reaction are then extracted and analyzed by GPC.

Example 4 - with polymer EG 2500

8 grams of LiV ₃ O ₈ , 0.43 grams of Ketjen carbon, 3.25 grams of EG-2500 polymer and 0.90 grams of LiTFSI are mixed with 27 ml of acetonitrile in a Jar Milling for 24 hours.

After evaporation of the acetonitrile at 80 ^° C., the measurements carried out and reported in FIG. 8 demonstrate the evolution of the molecular weight of the polymer EG-2500, under the same degradation conditions as the examples 2 and 3. figure also demonstrates, for this polymer, that the extracted cathode samples remain stable for a period of more than 2 hours at 80 ^° C. Subsequently, there is a decrease in the extraction rate and this, although the mass molecular weight and the polydispersity of the extractor remain stable. After more than one day, the polymer EG-2500 is fully crosslinked and shows no signs of degradation.

Only the by-products related to the crosslinking reaction are then extracted and analyzed by GPC.

Example 5 - P70 polymer with LiV ₃ O _δ oxide / pH less than 7

8.04 grams of LiV ₃ O ₈ and 0.43 grams of Ketjen carbon are dry blended mechanofusion for 45 minutes. The cobalt LiV ₃ Os-carbon thus obtained is mixed with 3.25 grams of polymer P70 and 0.904 grams of LiTFSI, to which 27 ml of acetonitrile are added; this mixture is introduced into a metal container 1/3 of which is occupied by the solution, 1/3 by volume steel balls and 1/3 of the volume is free. The coating is obtained by HEBM for 30 minutes at 25 ° C.

The solution is spread on an aluminum current collector using the Doctor Blade method. The electrode is dried under vacuum for 24 hours. The electrode obtained has a thickness of 45 microns. The battery assembly is performed as follows: Lithium / SPE / - P70 / LVO-P70.

The capacity of the cell is 5 mAh, the battery is maintained at 80 ^° C. for 2 weeks, in potentiostatic mode at 3.6 volts.

The capacity dropped by 25% (3.75 mAh), this loss of capacity is directly related to the dissolution of LiV ₃ O ₈ whose pH is less than 7.

Example 6 - 4-branch polymer with LiV ₃ O ₈ / pH 7

8.04 grams of LiV ₃ O ₈ and 0.43 grams of Ketjen carbon are dry blended mechanofusion for 45 minutes. This cobalt LiV ₃ O ₈ -carbon is mixed with 3.25 grams of the 4-branch polymer (Elexcel TA-210) and 0.904 LiTFSI, to which 24.7 ml of acetonitrile is added. The mixture thus obtained is introduced into a metal container of which 1/3 by volume is occupied by the solution of this mixture, 1/3 by steel balls and 1/3 of the volume remains free. The coating is obtained by HEBM for 30 minutes at 25 ° C.

The solution is spread on an aluminum current collector, by the method of Doctor Blade. The electrode is dried under vacuum for 24 hours, the electrode has a thickness of 45 micrometers. The battery is installed as follows: Lithium / SPE / -4Branches / LVO-4branches.

The capacity of the cell is 5.5 mAh, the battery is maintained at 80 ^° C. for 2 weeks in potentiostatic mode, at 3.6 volts. The capacity then measured is 5.2 mAh. The loss of capacity is 1% which is the limit of the error of the capacity. Which proves that LiV ₃ O ₈ is not dissolved.

Example 7 - EG with LVO - EG

8.04 grams of LiV ₃ O ₈ and 0.43 grams of Ketjen carbon are dry blended mechanofusion for 45 minutes. This cobalt LiV ₃ O ₈ -carbon is mixed with 3.25 grams of polymer EG 2500 and 0.904 LiTFSI, to which is added 45 ml of acetonitrile; this mixture is introduced into a metal container of which 1/3 by volume is constituted by the solution of this mixture, 1/3 by steel balls with a diameter of 6.34 mm and 1/3 volume remains free. The coating is obtained by HEBM for 30 minutes at 25 ^° C.

The solution is spread on an aluminum current collector, by the method of Doctor Blade. The obtained LVO-EG electrode is dried under vacuum for 24 hours. The electrode has a thickness of 45 micrometers. The battery assembly is performed as follows: Lithium / SPE-EG / - / LVO-EG.

The capacity of the cell is 5.5 mAh, the battery is maintained at 80 ^° C. for 2 weeks in potentiostatic mode at 3.6 volts.

The capacity then dropped by 25% (4.1 mAh). This loss of capacity is directly related to the dissolution of LiV ₃ O ₈ whose pH is less than 7.

Example 8 - P70 with LiFePO ₄ / pH greater than 7

8 grams of LiFePO ₄ and 0.45 grams of Ketjen carbon are dry blended mechanofusion for 45 minutes. This cobalt LiFePO ₄ -carbon is mixed with 3.25 grams of P70 polymer and 0.9 of LiTFSI, to which 45 ml of acetonitrile are added. This mixture is introduced into a metal container of which 1/3 by volume is filled with the solution of this mixture, 1/3 by steel balls with a diameter of 6.34 mm and 1/3 of the volume remains free. The coating is obtained by HEBM for 30 minutes at 25 ° C.

The solution is spread on an aluminum current collector, using the Doctor Blade method. The LiFePO ₄ -P70 electrode obtained is dried under vacuum for 24 hours. The electrode has a thickness of 45 micrometers. The battery assembly is performed as follows: Lithium / SPE-P707- / LVO-P70.

The capacity of the cell is 4.5 mAh, the battery is maintained at 80 ⁰ C for 2 weeks in potentiostatic mode at 3.63 volts.

The capacity then dropped by 27% (4.28 mAh). This loss of capacity is directly related to the non-stability in oxidation of the polymer P70.

When the battery is maintained at 80 ° C for 2 weeks, in potentiostatic mode at 4.00 Volts, the capacity drops by 51% (2.2 mAh). This loss of capacity is directly related to the non-stability in oxidation of the polymer P70.

Example 9 - 4 branches with LiFePO ₄ / pH greater than 7

78 grams of LiFePO ₄ and 0.45 grams of Ketjen carbon are dry blended by mechanofusion for 45 minutes. This cobalt LiFePO ₄ -carbon is mixed with 3.25 grams of polymer 4 Branches and 0.9 LiTFSI, to which is added 45 ml of acetonitrile; this mixture is introduced into a metal container of which 1/3 by volume is filled by the solution of the mixture, 1/3 of steel balls with a diameter of 6.34 mm and 1/3 of the volume remains free. The coating is obtained by HEBM for 30 minutes at 25 ° C.

The solution is spread on an aluminum current collector, using the Doctor Blade method, the LiFePO ₄ -4B electrode is dried under empty for 24 hours, the electrode has a thickness of 45 micrometers. The battery assembly is performed as follows: Lithium / SPE-EG / - / LiFePO ₄ -4B.

The capacity of the cell is 4.5 mAh. The battery is maintained at 80 ^° C. for 2 weeks in potentiostatic mode at 3.63 volts.

The capacity remains unchanged (4.5 mAh), the capacity maintenance is directly related to the oxidation stability of the 4-branch polymer.

When the battery is maintained at 80 ^° C. for 2 weeks in potentiostatic mode at 4.00 Volts, the capacity loss is 1% (4.45 mAh). This loss of capacity is directly related to the non-stability in oxidation of the polymer.

The maintenance of the capacity is directly related to the oxidation stability of the 4-branched polymer (4B).

Example 10 - 4 branches with LiFePO4 / pH greater than 7

78 grams of LiFePO ₄ , and 0.45 grams of Ketjen carbon, are dry blended mechanofusion for 45 minutes. This LiFePO ₄ -carbon cobalt is mixed with 3.25 grams of EG-2500 polymer and 0.9 grams of LiTFSI, to which 45 ml of acetonitrile are added. This mixture is introduced into a metal container of which 1/3 by volume is occupied by the solution of this mixture, 1/3 by steel balls with a diameter of 6.34 mm and 1/3 of the volume remains free. The coating is obtained by HEBM for 30 minutes at 25 ° C.

The solution is spread on an aluminum current collector, using the Doctor Blade method. The LiFePO ₄ -4B electrode is dried under vacuum for 24 hours, the electrode has a thickness of 45 micrometers. The battery assembly is performed as follows: Lithium / SPE-EG / - / LiFePO ₄ -4B. The capacity of the cell is 4.5 mAh, the battery is maintained at 80 ⁰ C for 2 weeks in potentiostatic mode at 3.63 volts.

The capacity remains unchanged (4.5 mAh). Maintaining the capacity is directly related to the oxidation stability of the 4-branched polymer.

When the battery is maintained at 80 ^° C. for 2 weeks, in potentiostatic mode at 4.00 Volts, the capacity loss is 1% (4.45 mAh). This loss of capacity is directly related to the non-stability in oxidation of the polymer.

Maintaining the capacity is directly related to the oxidation stability of the 4-branched polymer.

Example 11 - EG2500 with LiFePO ₄ / pH greater than 7

78 grams of LiFePO ₄ and 0.45 grams of Ketjen carbon are dry blended mechanofusion for 45 minutes. The resulting LiFePO ₄ -carbon cobalt is mixed with 3.25 grams of EG-2500 polymer and 0.9 of LiTFSI, to which 45 ml of acetonitrile are added. The mixture thus obtained is introduced into a metal container of which 1/3 by volume is filled with the solution of this mixture, 1/3 by steel balls with a diameter of 6.34 mm, and 1/3 of the volume. remain free. The coating is obtained by HEBM for 30 minutes at 25 ° C.

The solution is spread on a 17 μm thick aluminum current collector, using the Doctor Blade method. The LiFePO ₄ -4B electrode is dried under vacuum for 24 hours, it has a thickness of 45 micrometers. The battery is installed as follows: Lithium / SPE-EG / - / LIFEPO ₄ -polymer 4B.

The capacity of the cell is 4.5 mAh. The battery is maintained at 80 ^° C. for 2 weeks in potentiostatic mode at 3.63 volts. The capacity remains unchanged (4.5 mAh), the capacity maintenance is directly related to the oxidation stability of the 4-branch polymer.

When the battery is maintained at 80 ⁰ C for 2 weeks in potentiostatic mode at 4.00 Volts, the loss of capacity is 1% (4.45 mAh). This loss of capacity is directly related to the non-stability in oxidation of the polymer.

The maintenance of the capacity is directly related to the oxidation stability of the EG polymer.

The coated particles of the invention are found to have excellent electrochemical properties, especially with regard to the life of batteries in which they are incorporated and because of its economic interest.

Figure 1 illustrates the phenomenon of dissolution observed for small particles, uncoated, based vanadium oxide lithia and LiVaO ₈ . The insertion of Li into the vanadium oxide causes a volume increase of the particles; at the origin of an average size of 5 micrometers (D50). The lithiated particles have an average size of 5.5 micrometers (D55), which corresponds to a size increase of 3 to 4%. After 50 cycles, the metal oxide particles have a smaller average size of 3.5 microns.

Figure 2 illustrates the phenomenon of dissolution of large particles, uncoated, based vanadium oxide lithiated. The insertion of Li into the vanadium oxide causes a volume increase of the particles. The lithiated particles have an average size of 33 micrometers. After 100 cycles, the metal oxide particles have an average size of 23 micrometers. Figure 4 shows the behavior of an electrode according to the invention, wherein the particles of the metal oxide have been coated with a stable polymer which slows the dissolution of vanadium in the electrode. The references used in FIG. 4 are: 18 for lithium, 20 for SPE, 22 for Ketjen carbon, 24 for (4-arm polymer) coating the oxide and 5 for oxide core.

Although the present invention has been described with the aid of specific implementations, it is understood that several variations and modifications can be grafted to said implementations, and the present invention aims to cover such modifications, uses or adaptations of the invention in general, the principles of the invention and including any variation of the present description which will become known or conventional in the field of activity in which the present invention is found, and which can be applied to the essential elements mentioned ci -high.

Claims

claims

1. Particle comprising a core and a coating which covers at least partly, preferably at least 80%, more preferably still at least 90% and in the most advantageous manner 100% of the surface of said core, said particle being characterized in what:

said core is preferably composed for at least 90%, more preferably still for at least 94% by weight of an acid metal oxide, with a pH of preferably less than 6.5, more preferably still with a pH of between 3 and 6;

- The coating of the core being based on a polymer, preferably based on a salt polymer, whose electrochemical stability is greater than or equal to 3.7 volts;

the size of the coating is of average thickness preferably between 500 nanometers and 2 micrometers and the coated core is of an average size of ₅₀ which is preferably between 500 nanometers and 40 micrometers, more preferably still this size is between 2 and 20 micrometers; and

the solubility rate (ts), at a fixed time, of the metal oxide migrating towards the electrolyte, per cycle, is less than 5 per 10,000, preferably this level is between 2 and 4.5 per 10,000.

2. Particle according to claim 1, characterized in that the polymer used to carry out the coating is chemically stable.

3. Particle according to claim 2, characterized in that the polymer used to carry out the coating is chemically very stable.

4. Particle according to claim 3, characterized in that the polymer used to carry out the coating is chemically extremely stable.

5. Particle according to claim 4, characterized in that the electrochemical stability of the polymer used for the coating is between 3.75 and 5 volts.

6. Particle according to any one of claims 1 to 5, wherein the metal oxide is selected from the group consisting of LiMn ₂ O ₄ , V ₂ Os, LiMn ₍ 2-χ) V _x θ 4 with x varying from 0 to 1 terminals inclusive, V ₆ Oi ₃ and LiV ₃ Os _{, more} preferably the metal oxide is LiV ₃ O ₈ .

7. Particle according to any one of claims 1 to 6, wherein the core of the particle comprises from 1 to 12%, preferably from 6 to 10% by weight of a carbon chosen preferably from the group consisting of ethylene black, natural graphite, artificial graphite, Shawinigan carbon, Ketjen carbon, and mixtures of at least two of these.

8. Particle according to any one of claims 1 to 7, wherein the coating of the core is based on:

one or more salt polymers, preferably based on at least one polymer salted with at least one salt selected from the group consisting of salts of LiFSI, LiTFSI, LiBETI, LiDCTA, LiBF ₄ and LiPF _{6 type} ; and

at most 10% of fillers chosen preferably from the group consisting of SiO ₂ , ZrO ₂ and Al ₂ O _3, and mixtures of at least two of these.

9. Particle according to any one of claims 1 to 8, wherein the polymer constituting the coating is electronically conductive, and it is preferably based on a polymer selected from the group consisting of polyanilines, preferably in the group of polyanilines having an average molecular weight greater than 1000, and preferably between 2500 and 50000.

10. Particle according to any one of claims 1 to 9, wherein the polymer constituting the coating is nonconductive electron and it is preferably chosen from the group consisting of non-conducting polymers of the multi-branch type.

11. Particle according to claim 10, wherein the electron-non-conductive polymer is at least 3 branches, and more preferably still of the 4-branch type such as those described in the international application WO 03/063287 (and more particularly on pages 5, 5). 8 and 9), filed in the name of Hydro-Québec, as well as in columns 1 and 2 of US Pat. No. 6,190,804 and which have hybrid acrylate (preferably methacrylate) and alkoxy (preferably alkoxy) terminators with 1 to 8 carbon atoms, more preferably still methoxy or ethoxy), or vinyl.

The particle of any one of claims 1 to 11, wherein the metal oxide is a mixture (50:50) of LiV ₃ O ₈ and V ₂ Os.

13. Particle according to claim 1, comprising a core of the metal oxide LiV ₃ Os of a size of 5 microns, covered for 80% of its surface by a coating consisting of the polymer type 4 branches and an average thickness between 10 nanometers and 5 micrometers, preferably between 15 nanometers and 2 micrometers, characterized by an ts less than 5%.

14. Particle according to claim 1, comprising a core of the metal oxide V ₂ O ₅ of a size of 5 microns, covered for 80% of its surface by a coating consisting of the polymer 4B and of an average thickness between 10 nanometers and 5 micrometers, preferably between 15 nanometers and 2 micrometers, characterized by a ts less than 4%.

Process for the preparation of a homogeneous mixture of particles according to any one of Claims 1 to 14, by preparing a mixture of the polymer and a metal oxide, by the dry route without any addition of solvent, preferably in proportions by weight of 10 to 90%, preferably 40 to 80% for each of the constituents of the mixture, preferably the amount of metal oxide present in the mixture is greater than that of the polymer.

Process for the preparation of a homogeneous mixture of particles according to any one of Claims 1 to 14, in which the mixture is:

- by preparing a mixture of the polymer and a metal oxide, preferably in proportions by weight of 10 to 90%, preferably 40 to 80% for each of the constituents of the mixture, preferably the amount of oxide metal present in the mixture is greater than that of the polymer; and

with addition to the solvent of at least one solvent selected from the group consisting of acetone, acetonitrile, toluene, MEK, NMP or mixtures of at least two of these, preferably the solvent used represents in volume of 10 to 80%, more preferably 20 to 70% of the total volume of the solvent and the mixture.

17. The method of claim 15 or 16, wherein the mixture is milling, sand mill, HEBM, mechanofusion, agglomaster, Nobita ^® or by using at least two of these techniques and preferably at a temperature. between 10 and 40 ^° C. and, preferably, in the presence of an inert gas selected from the group consisting of nitrogen, argon or dry air.

18. An electrode consisting of an electrode support, said support being preferably made of a metallic material or a conductive plastic material, and at least partially covered, preferably homogeneously by a mixture of at least 40%, preferably 50 to 80% by weight of particles defined in any one of claims 1 to 14 or obtained by one of the processes defined in any one of claims 15 to 17.

The electrode of claim 18, wherein at least one polymer is a binder of said electrode by creating bridges between the electrode support, the metal oxide particles and the polymer coating.

20. An electrode according to claim 19, wherein the binder polymer is a mixture of a high stability polymer and binder and a polymer which provides the connection between the particles of the cathode and which is different from the polymer present in the coating.

21. An electrode according to claim 19, wherein the binder polymer consists solely of the coating polymer with high electrochemical stability.

22. Electrode according to any one of claims 18 to 21, comprising at least one polymer containing at least one lithium salt and at least one carbon of specific surface area greater than or equal to 1 m ² / g, preferably at least one carbon. specific surface area greater than 50 m ² / g.

23. Electrode according to claim 22, wherein the mixture (polymer-oxide-salt-carbon) has been produced without addition of solvent, preferably by implementation of the method of Doctor Blade and / or by extrusion.

24. Electrode according to claim 22, in which the mixture (polymer-oxide-salt-carbon) has been produced with the addition of a solvent preferably chosen from the group consisting of acetone, acetonitrile, toluene, MEK, VC. , DEC, DMC, EMC, DME or mixtures of at least two of these, preferably by using the method of the Doctor Blade and / or by extrusion.

25. The electrode of claim 23 or 24, wherein the polymer composition is 1 to 70% by weight relative to the total weight of the mixture (polymer + salt + oxide + carbon).

26. Electrode according to claim 25, wherein the composition of the carbon represents 1 to 10% by weight relative to the total weight of the mixture (polymer + salt + oxide + carbon).

27. An electrode according to any one of claims 18 to 26, wherein the concentration of the salt, present in the mixture (polymer-oxide-salt-carbon), and expressed with respect to the polymer, is between 0.1 M and 3 M, preferably between 0.7 M and 2 M.

28. An electrode according to any one of claims 18 to 27, wherein the carbon present in the mixture (polymer-oxide-salt-carbon) is a mixture of a first carbon of graphite nature with a specific surface area less than 50 m ² / g and a second carbon type large non-graphitic surface whose specific surface area is greater than 50 m ² / g, the specific surface area being measured according to the BET method.

29. Electrode according to any one of claims 18 to 27, wherein the carbon is carbon fiber type VGCF, mesophase Ex, PAN

(Polyacronitryle).

The electrode of claim 29, wherein the salt is dissolved in the polymer and is selected from the group consisting of LiFSI, LiTFSI, LiBETI, LiPF ₆ and mixtures of at least two of these.

31. A method of preparing an electrode according to any one of claims 18 to 28, wherein an oxide-polymer-salt-carbon liquid mixture is spread on a metal-type current collector by extrusion or Doctor Blade slot die, coma.

32. A method for preparing an electrode according to claim 31, wherein the polymer is of the four-branch type with preferably at least two branches capable of giving rise to crosslinking, and is converted into a polymer matrix, optionally presence of an organic solvent, by crosslinking after spreading the mixture on the electrode support.

33. The method of preparing an electrode according to claim 32, wherein the crosslinking is conducted without adding a crosslinking agent other than the metal oxide.

34. A process for the preparation of an electrochemical generator comprising at least one anode, at least one cathode and an electrolyte, in which at least one of the electrodes is as defined in any one of claims 18 to 30, or such that obtained by one of the methods defined in any one of claims 31 to 33.

35. A method of preparing an electrochemical generator according to claim 34, wherein the electrochemical generator is of the lithium generator type and the spread cathode is introduced into said lithium generator with a dry polymer as electrolyte, the battery contains no solvent. liquid.

36. A method of preparing an electrochemical generator according to claim 35, wherein the electrolyte is made of the same material as the binder and the coating.

37. A method of preparing an electrochemical generator according to claim 35, wherein the electrolyte is made of a material different from that which constitutes the binder and / or the coating.

38. A method of preparing an electrochemical generator according to any one of claims 34 to 37, wherein the electrolyte also has the role of separator and consists of a dry polymer which has an electrochemical stability greater than 3, 7 Volts.

39. A method of preparing an electrochemical generator according to any one of claims 34 to 37, wherein the electrolyte also has the role of separator and consists of a dry polymer which has an electrochemical stability of less than 3, 7 Volts.

40. Process for the preparation of an electrochemical generator according to claim 34, in which the anode is of lithium or lithium or carbon alloy type, graphite, carbon fiber, Li ₄ Ti ₅ Oi ₂ , WO ₂ , preferably lithium metal or slightly alloyed.

41. A method of preparing an electrochemical generator, according to claim 40, wherein the lithium is alloyed with Al, Sn, carbon, Si, Mg and the alloy metal content is greater than 50 ppm, preferably greater than 500 ppm. .

42. An electrochemical generator obtained by implementing one of the methods according to any one of claims 31 to 41.

43. An electrochemical generator containing at least one constituent element comprising particles as defined in any one of Claims 1 to 14 or as obtained by implementing a method according to any one of Claims 15 to 17.

44. Generator obtained by implementing one of the methods defined in any one of claims 36 to 41 or as defined in claims 42 or 43.

45. Use of a generator according to claim 44 in an electric vehicle, in a hybrid vehicle, in telecommunications, UPS, and in electrochromic devices.

46. A process for preparing an electrode according to claim 31, wherein the polymer is of EG type, with preferably at least two branches liable to give rise to crosslinking, and said polymer is converted into a polymer matrix, possibly in the presence of an organic solvent, by crosslinking after spreading the mixture on the electrode support.

47. Process for reducing the solubility of metal oxides in electrochemical systems consisting in increasing the pH of the oxide, preferably by choosing the nature and the quantity of the carbon mixed with the oxide particles, more particularly by coating the particles of is oxidized by a polymer, based on PEO, polyacrylonitrile, PMMA and / or PVC solubilized in a solvent (acetonitrile, water, acetone, methanol, etc.), then drying the composition and carbonizing it at a temperature of 600-700 ^° C. under an inert atmosphere for 8-12 hours; the quantity and type of the polymer used being connected to the residual carbon content present at the surface of the particles of the oxide and the oxide and polymer solution mixture can be advantageously produced by jar mill, bar mill, or paint mixer.